EghtesadOnline: The Foreign Ministry summoned Britain’s ambassador to Iran after British forces seized an Iranian oil tanker in the Strait of Gibraltar, bordered by Spain and Morocco.

Rob Macaire was summoned to the ministry on Thursday, hours after reports emerged that the vessel had been boarded by British Royal Marines and impounded, IRNA reported.

"We declared to the ambassador that this move amounts to a peculiarly unconventional and Iran denounces the seizure as a destructive step, which contributes to further escalation in regional tensions,” Financial Tribune quoted the Foreign Ministry’s spokesman as saying.

Abbas Mousavi added that it is "a form of piracy", does not have any legal and international bases, and showed that Britain was toeing "the hostile policies of the US".

Acting Spanish Foreign Minister Josep Borrell said on Thursday Gibraltar detained the supertanker Grace 1 after a request by the United States to Britain.

Borrell noted that Spain was looking into the seizure of the ship and how it may affect Spanish sovereignty, as it appears to have happened in Spanish waters. Spain does not recognize the waters around Gibraltar as British.

White House national security advisor, John Bolton, said the seizure was "excellent news", saying the tanker laden with oil bound for Syria was violating EU sanctions.

The US has vowed to reduce Iran’s oil exports to zero as part of the sanctions it reinstated after leaving a multilateral nuclear deal with Iran last year. However, unlike the United States, Europe has not levied broad sanctions against Iran.

According to the Telegraph, Macaire told the Iranian Foreign Ministry that the move was about enforcing sanctions on Syria, not on Iran, and that Britain views Iranian oil exports in general as legitimate.

While Europe has banned oil shipments to Syria since 2011, it had never seized a tanker at sea.

Lloyd's List, the shipping publication, said the 300,000-ton Panamanian-flagged tanker loaded oil off Iran in April before sailing around the Cape of Good Hope, a lengthy route was apparently taken because the ship was too heavy to use the Suez Canal.

Tanker Hostage by Saudis

Iranian officials have warned Saudi Arabia against holding an oil tanker "hostage", describing it as an "illegal seizure" and a case of "ransom-seeking" aimed at gaining concessions from Iran.

On May 2, Saudi Arabia announced its coast guard had “rescued” a distressed Iranian oil tanker, named Happiness I, with 26 on board off the Red Sea port of Jeddah, after it faced "engine failure and the loss of control."

Two months on, despite being fixed, Saudis are refusing to let the vessel leave, and at the same time charge Iran $200,000 a day for maintaining the vessel in Jeddah, Mehr News Agency reported.

So far, over $10 million have been paid to the port authority in Jeddah for maintenance costs but despite the full payment, Saudi officials have refused to let the ship return to Iran.

Oil Minister Bijan Namdar Zanganeh told reporters on Wednesday that Iranian officials at the National Iranian Tanker Company are following up the fate of the vessel and the problem will be solved soon.

"The issue has financial costs for Iran, but we are more concerned about a possible environmental disaster in the region," he said.

Iranian officials say the incident occurred on April 30 while Happiness I was on its way to the Suez Canal and that water had leaked into the tanker’s engine room. It has been reported that all necessary precautions were taken to avoid any environmental damage.

TankerTrackers monitoring group estimated the vessel was carrying up to 1.22 million barrels of crude oil.